Homogeneous Charge Compression Ignition (HCCI) and Premixed Charge Compression Ignition (PCCI) are known processes for fueling a compression ignition (i.e., diesel) engine in a manner which creates an air-fuel charge inside an engine cylinder during a compression upstroke of an engine cycle. After creation of the charge, the increasing compression of the charge by the upstroking piston creates sufficiently high temperature to cause auto-ignition of the charge. The fuel which is used to create the charge may comprise a mixture of different reactivity fuels. Gasoline, natural gas, and ethanol are examples of low reactivity fuels while conventional diesel fuel is an example of a high reactivity fuel.
The HCCI mode of operation of a diesel engine is significantly affected by chemical kinetics, thwarting the ability of even the best controls and devices, which are capable of injecting fuel at different injection pressures, at different times, and for different durations during an engine cycle, to properly control combustion events in ways that would enable engine performance and emission targets to be met over the full operating range of the engine.
PCCI is similar to HCCI in that fuel is premixed with air but the resulting mixture is less homogeneous. Stratified Charge Combustion Ignition (SCCI) is another similar type of combustion but is premised on some degree of stratification of a premixed charge.